The present invention relates to an apparatus for measuring lengths or angles. The apparatus comprises a carrier for graduations, including a first incremental graduation having equal intervals as well as other graduations for obtaining values of positions with respect to a zero position. This apparatus also comprises a sensing and evaluating circuit with a sensor device that is movable with respect to the carrier, for sensing the graduations.
Known apparatus of this type have various types of graduations for obtaining absolute measured values with respect to a zero position. German Patent Application DE-A1 No. 3039483 (Heidenhain GmbH) discloses a carrier having an incremental graduation as well as a track of reference marks and a code track. The marks of the code track are used to identify the respective reference marks. German Patent DE-C No. 2416212 (Contraves) discloses a carrier having an incremental graduation as well as a track of absolute marks. Each absolute mark has its own distance from the next following one, this distance characterizing the distance of that mark from a zero position.
One object of the present invention is to provide an apparatus for measuring lengths or angles with a carrier having only graduations with equally distant marks, and operating such that a determination of absolute distance from a zero position is possible by scanning only a limited part of the total graduation just as one does with coded marks.